Secret signaling system



April 24, 1945.

M. MORRISON 'SECRET SIGNALING SYSTEM Filed Sept. 1 8, 1943 2 Sheets-Sheet 1 I N V EN TOR. ff/W pxr 24, i945. M. MORRISON 2,374,495

SECRET SIGNALING SYSTEM Filed .Sept 18, 191,: 2 5.2; 'et 2 IN VEN TOR.

Pate'nted Apr". 24, 194s UNTTED STATES PATENT OFFICE SECRET srGNALlNG SYSTEM Montford Morrison, Upper Montclair, N. Application september 18,1943, serial No. 502,893

' 9 claims. (ci. 11s-s6) The presentl invention relates to signal Wave transmission and signal wave reception, in which.

which is not subject to code detection by any receiverof the prior art; to provide such a system that is capable of operation in any of the known nediatof wave propagation and to provide such a system that is simple in structure and dependable in operation.

The spirit of this invention may be employed in, or applied to, systems of signaling by means oi sound waves through air, solid media or through Water, by means of electric waves of current through a conducting medium, by means of magnetic induction waves through space and other media, by lightI waves through translucent media and by any other means capable of wave propagation.

A specic object of this invention is ,to provide a system of signal'transmissi'on for code work, in which the reception is not as much subject to interference as in the ca'se of amplitude modulation systems and therefore the invention is par ticularly suited to equal unit code transmission and reception, such as the Baudet code used in mechanical teleprinter operation, which is extensively known to be critically subject to amplitude interference, Y A

In the prior art of code signaling by wave motion where phase modulation has been employed, a carrier-wave usually displaced 910 electrical degrees from the original carrier position is propagated with the modulated wave'so that phase detection is possible at the receiving station. Without the reception of a correlated carrier-wave,

detection of phase modulation is not possible.`A

In this statement the word carrier-wave may be construed to be any frequencyvby which the phase of the modulation in the detector circuit may be determined. s e

In the present system, the carrier frequency or in eiiect the reference frequency by whichlthe this invention in its broadest terms and with its greatest renements of engineering detail, this disclosure will be limited to a simple embodiment of an operative structure which is well suited to teaching the art without extensive engineering refinements. k

One of the principal spirits of the invention resides in the fact that the transmitting medium may have but a single frequency transmitted through it at a constant amplitude with only a slight phase shift due to signal modulations therein. Such a transmitted wave is not subject to signal detection by any vreceiver of the prior art and therefore, since the present receiver is a highly specialized device, the secrecy of such a method of transmission is of a high order and for all practical purposes absolute in the absence of a proper receiver.

It is not claimed that the directional proper- I ties of the transmitter are secret but only the modulation character of the transmitted wave. Further features and other objects will be apparent after reading the following description, y

is a series of graphs illustrating the operation ofv the system steps.

Referring to Fig. l, i is a source of constant frequency, which may be an electrically driven tune fork, which may have any degree of constancy up to vone part in 1,000,000 and of which there are common examples on the market in use in watch recorders having an accuracy of one part of 100,000. E is a loading device which may be imposed upon source i by closing switch 3.

It will be appreciated by those skilled in the art that the period of any oscillatory system can be increased. in length or the frequency may be decreased, inyother words, the system may be made to oscillate at a slower rateby the imposition additional loading.

The oscillating system i runs at a highly standardized frequency with the switch opened and with the switch d closed, the oscillating system is loaded Just sumcienuy that it cannot drift into a higher frequency than its standardized operating limit, the full purpose of this will be fully brought out hereafter.

The apparatus enclosed in area 4 is shownv as a simple relaxation oscillator having two gaseous triodes 5 and t. The relaxation circuit is trggered by either one ot the said triodes 5 and 6 and the plate current from the said triodes servinthe area I.

With the switch 3 `opened .and the switch 'I closed,fthe output voltage of the oscillator I is fed through the tuned amplifier 8, through the negatively biased rectifier 9, which serves to trigser the gaseous triode 5.

Referring to Fig. 2, the curve along the abscissa A represents the input voltageof rectifier 8, Fig. 1. The'curve IIIy along abscissa B, Fig. 2. represents the output of negatively biased rectifier 9, that is, rectier 9 is Aa fullA wave negatively lconnected rectiiier having considerable negative bias.`

By employing such a method the gaseous triode 5 is triggered by voltage points shown at I I, Fig. 2, which occur at the zero position of the alternating current wave, giving a high precision yof phase position `between .the triggering voltage of the f f f Referring to Fig. 2, the curve along the abscissa mitted having a highly accurate fixed phase posif f f tion with'reference to timeand space and when the key I5 isv in they down-position this same wave is transmitted but withv its phase positiony shifted f f f backward,'with reference to time.

G, identified by I6, would represent ther phase position of the transmitted wave of the up-position of key I5 and wave l1 would represent theA f f actly the same frequency.

triodesr andftheir output currents; It will beape preciated that in all synchronizing ymethodsy in `which an-unrectifled sine wave is utilized to lock infcircuits, the locking position is necessarily an indeilnite one, due to the locking point being-inf f *determinate by reason^of the various different ratesofchange in the slope of the applied sine curve.

fixation is achieved.

art, upony inspection of the curve. l As will be pointed out further on, in the present embodiment I only use every other zero point in curve i9 and the intervening points-are useless. but the description ofthefoperation will be limited to that without the use of curve l2.

Curve I3, Fig. 2, along the abscissa C represents the familiar saw-tooth voltage of the relaxation oscillator 4 and the show period impulses along abscissa D represent the driving current supplied to oscillator I. D

It is appreciated by those skilled in the art of accurate timing, that any oscillating system more closely follows its own natural period and is less influenced to force oscillations, the shorter the period that the driving energy is applied to the system, so that this method of short impulse driving power for oscillatorL i, is conducive to a high order of constancy of frequency in the oscilf lator shown in area l, by the same token .that this is true in astronomical pendulums.

With the oscillator l operating at its standardized frequency. and with I8 closed, the output oi tuned amplier 8 is fed to the phase modulatiorr device i4, which in the present case consists of a push-pull circuit with the tubes operating 90 out of phase and means for cutting'in and out one or the other by a device such as a telegraph key I5. The output of phase modulator Il is fed into an amplifier and wave transmitter, as shown in Fig. 1. y

As stated in the beginning of the specification, this wave transmitter may be any means whatever to convert the phase modulated current-wave into any of the types of propagated waves thereabove mentioned.

If the present invention is employed as a submarine signaling device the wave transmitter can then be one of the several sound wave transmit- In the present method, the locking posi-y f tion being at thezero point, this indeterminate f yposition is eliminated and a highly accurate phase In the methodmf modulation employed, rthere f f n `is no energy transient in the modulation circuit properandonly an infinitesimal energy transientin the system as a whole and since rthis transient n l n occurs in such a short period of time with refervence tothe signal length it is imperceptiblein prior art detection systems. f f f f y The method of transmission then isa simple f one of transmitting a wave `of a single-frequency and shifting it back and forthwith respect to time, at the modulation points.

When Fig. 1 is to be utilized as a receiver of such a wave as has been described, the trans-y mitting circuit may be electrically disconnected from the oscillator by opening switch I8, leaving switch 'l open and closing switch 3, the oscillator I kbeing now at rest since no driving energy is being received by it.

. transmitter similar to I4, is received by wave receiver i9, the resultant current passes through tuned amplifier 2li.' yBy closing switch 2|, the received wave is fed through the negatively biased rectiiler 22, which in turn operates the gaseous triode tube 6 in' an exactly similar manner to that heretofore described for the circuit connected with gaseous triode 5, the difference being that oscillator I, under this set of conditions, is, by the principle of forced oscillation, made to not only follow the frequency of the incoming wave but adjust itself perfectly to its relative phase position.

ln this way .oscillator I is forced to assume the phase position of the transmitted wave sent out by the wave transmitter from a distant station, having a phase position corresponding to the up-p'ositin to the key I5 in Fig. l, in the distant station. Thus the phase position of the unmodulated wave from the transmitting station is v wave 'it will follow its frequency and phase posi-v tion even with the switch `3 closed, as is now its position, as is understoodl by those skilled in the art. l

However, upon closing switch 1, the oscillator will follow whichever triggering voltage point occurs first.

Referring to Fig. 2. curve C, afterthe voltage f the relaxation oscillator has been triggered as shown in curve Il, the value of this voltage drops to such a low point sokrapidly that any'subsequent triggering voltage has no effect upon it until the voltage has had time toregain nearly its maximum value. y,

If, after oscillator I has been phased with an unmodulated incoming wave and if switch 2| were the phase position of oscillator I, and oscillator I will continue to oscillate in its original phase position with the exception of the slight drift backward. i

When the received wave is reestablished to the unmodulated phase position of the standardized oscillator in the distant station, gaseous triode 6 again takes control of the phase position oscillator I and'reestablishes it back in its standardized position. This will be more fully understood with reference to Fig. 2 in which curve I0, ab-

scissa B, represents the triggering voltage-of both triodes 5 and 6, when the triggering voltages are in phase and therefore illustrated bythe single curve I0. This represents the case when the key in the distant station is in the up-position.v

When the key in the distant sending station is in the down-position, the triggering voltages are represented along abscissa H, Fig. 2, curve I0 remaining in the same phase position andcurve 23 being shifted 90 behind curve I0. Because of the fact of the voltage drop in curve I3, abscissa C, Fig. 2, and its subsequent slow rise, this voltage does not reach a value which will permit the tubes to be triggered by any subsequent triggering voltage .until a. complete cycle has elapsed. In other words, only at points 24, 25 and 42li, abscissa H. E

In fact, however, for long periods of holding the key I5 in the down-position the local oscillator I will have a. tendency to drift slightly, as illustrated along abscissa F by the curve 27, which is slightly behind the relative standardized position so that when the key in the distant station is returned to its up-position and the transmitting wave is advanced to its standardized phase position, the triggering voltage on triode S will be slightly ahead of the triggering voltage for triode 5 and which advanced .position is illustrated by curve 28, abscissa F, Fig. 2. In this Way the phase position of the oscillator is returned to its standardized position, or as it is referred to in telegraph engineering, it is in this way corrected.

Between the local oscillator circuits and the receiving circuit is a two-channel mixer amplifier 25, supplied with a translating device 36. These mixing channels are so constructed that when the key in the distant sending station is in the upposition, the voltages in the translating device 3G exactly neutralize each other,as is shown along abscissa E, Fig. 2. When the key is in the downposition at the distant transmitting station, the phase position of the input side 3l of the amplilier 29 remains substantially in its original phase position, as can also be illustrated by curve I6, Fig. 2, and the voltage across the channel 32 of ampller 29 is shifted back to a position which can also be illustrated by curve I'I, Fig. 2', the vector sum of which is illustrated by curve 33, which represents the signal current in translating device 30, which is present under the system of operation for the key in the distant sending station in the down-position and the current in translating device being vsubstantially zero with the key in the up-position, as above explained.

It will be appreciated by those skilled in the art,

that the phase correction method herein described is obviously applicable, without invention, to amplitude modulation wherel phase shift is not employed.

It willfbe further appreciated by those skilledl in the art, that the present'invention when embodied in a voice frequency carrier code telegraph system, may be further modulated upon a second carrier-wave, such as a radio frequency carrierwave, by well known engineering procedure without further invention.

The term carrier" as employed herein, is here by defined to mean that prime unmodulated frequency which is employed in the transmitter in fixing the modulation characteristics of the signal frequencies transmitted and the corresponding prime unmodulated frequency which is employed in the receiver to determine the -modulation characteristics of the signal frequencies received,

The foregoing description has been limited to a simple embodiment well adapted to teaching the spirit of the invention but the scope thereof is covered in the claims hereunder.

What I claim is: y

1. In a carrier phase-modulated-wave communication system in combination, sending terminal equipment for transmitting one frequency of wave propagation, when modulated, modulated by absolute phaseposition, a transmitting path to a receiving station, receiving terminal equipment including a local oscillator to determine the modulation of the received signal wave, the phase position of said oscillator being responsive to the unmodulated phase position of said wave and to the unmodulated position only, and detection means responsive to the modulated position of said wave.

2. In a telegraph signal system receiving terminal equipment in combination, a local alternating current generator for timing in the reception current, a source of periodic current for driving said generator, said source being provided with two timing elements, each and either, for xing the period thereof, and said source being responsive to either timing element during any one tim-A ing period thereof but not responsive to both during any one timing period thereof.

3. In a telegraph signal system receiving terperiod of said current, one of said timing elements being responsive to the frequency of the signal current received, the other of said timing elements being responsive to the said source per se, and frequency of the said source being determined by either timing element during any one timing period thereof but not determined by both timing elements during anyone timing period thereof.

4. A system of phase-modulated carrier-wave transmission and reception having station terminal equipment for transmission of signals at a predeterminedwave frequency, a transmitting medium, station terminal equipment forv reception o f signal waves including a local oscillator having its phase position corrected by said carrier-wave during periods of unmodulated carrier- Wave reception, and means in said equipment than that of first said' frequency during periods ot.

` ing and spacing signals through a transmitting medium, transmission and reception equipment, and detection means in said reception equipment including a local oscillator corrected during reception of said marking signals and during said reception only.

7.111 a system of phase-modulated carrierwave transmission and reception providing marki ing and spacing signals through a transmitting' medium, transmission and reception equipment, and detection means in said reception equipment including a4 local oscillator corrected during re caption of said spacing signals and during said reception only.

8. En a phase-modulated carrier-wave communicatiori system operating at a predetermined 3@ transmitting frequency in combination, trans-- mitting terminal equipment for phase modulation of said carrier-wave, a transmitting path to a receiving station, receiving terminal equipment in-v cluding a local oscillator free of correction to operate at a frequency less than aforesaid frequency during the reception of modulated signals, and means in the receiving terminal equipment for correcting the frequency of the said' local oscil lator during the reception of unmodulated signais.

9. In a system of phase-modulated carrierwave tranmission andreception having station terminal equipment for transmission and reception of signals, transmission terminal equipment for the generation and transmission of a carrierwave having a fixed time phase position, means in last said terminal equipment providing modulated time phase position tranmission o1' said carrier-'wave under signal operation, a transmitting medium, reception terminal equipment including a local oscillator for the detection o! last said transmission, and means in last said equipment providing the correction of said oscillator by received carrier-waves having said xed time phase position and providing operation oi' said oscillator free 'of said correction by said carrierwaves having modulated time phase positions.

i MONTFORD MORRISON. 

